Fire detector



Dec. 20, 1955 Q 1 ADAMS ET AL 2,728,068

FIRE DETECTOR Filed May 19, 1949 2 Sheets-Sheet l KQ/Ww Dec. 20, 1955 c. J. ADAMS ET AL 2,728,068

FIRE DETECTOR Filed May 19, 1949 2 Sheets-Sheet 2 2,72s,s6s FIRE DETECTOR Charles J. Adams, Park. ld-ge, and blohn. A. Proctor,

Chicago lll..assig'norsto- American Phenolic Corporation, Chicago, lll., a corporation of Illinois Application May 19, 1949, seriaiNo. 94,222 19 claims. (ci. 34a- 227) The present invention relates to tire directors. The specic form of the invention here disclosed is particularly designed to detect tires in the engine nacelles of aircraft, but the detector is also suited to other uses, asfor protecftionof grain elevators or coal'piles against spontaneous combustion, or safeguarding warehouses or other build,- ings. In any case it is the function of the detector to give an almost instant visual or aural alarm of the outbreak of a re, and, if desired, to initiate the operation of an automatic fire extinguishing system. K, K

It is theV general aim or the invention ,to provide a reliable, quick acting detector to perform this function. Thel accomplishment of this aim involves manyV aspects, however, since4 to achieve the requisite degree of reliability the detector must operate perfectly in any position, be' impervious to forces of acceleration and deceleration, be capable of uniform operation Within extremely wide limits of temperature, altitude and humidity, and mustbe unaffected by continued vibrations, physical shock, .or long exposure to all manner of adverse conditions', includingV corrosion resulting from rain, salt spray, immersion in fuel or oil, as well as exposure to violently blown dustand sand. The problem of providing a satisfactory lire detector, particularly one suited for aircraft use, is further 2,728,068 Patented Dec. 2o, 1955 22' than` functioningr only' at one or more separate points. This is because Vthe Widely variable ambient `temperatures which the devices vare subjected ordinarily alect the entire length of any continuous detecting unit, While the flame Aof an actual fire may only inuence a small portion of a continuous detector. e A l It is, therefore, one o f the primary objects of tion to provide a fire detecting device adaptedl to be mounted in the engine compartment of an aircraft, for example,andcapab1e of giving an almost instant signal ifafire develops lin the engine, yet wholly unaffected byA ambient temperature changes, so that the time required for response to a tlame will remain substantially constant over a range of several hundred degrees in ambient temperature. e e Y Another important object of the invention isv to provide a lire detector capable of giving an unfailing signal Within compartment, andat the same time structed1 thatjt Willl continue to function even when its partfsl lare heated almost toincandens'cence. This means that' the detector will continue to function presence of the lire, lso that the termination of the detectorlalarm signal gives a reliable indication that the rejlias been extinguished.

Y A further object of the invention is the provision of a` fire detector havingthe functional characteristics noted and additionally capable of repeated operation even after exposure' to tire andfto terrific extremes in sub-zero temperatures. The accomplishment of this object means that and in condition for proper lire develop.

humidity or thepresenceof dust or violently driven sand, and not in any manner aiected by rain, salt spray, acids, or immersion in lfuel or lubricating oil.

A nfurther object' of the invention is the provision of a tire detector as above with sensing means of the continupoints of sensitivity spaced apart from each other.

A still further object of the invention is to provide a fire detector having relatively long, continuous sensing means of extremely small cross section and high physical flexibility, so that the armsmay be conveniently coiled Within an engine nacelle, for example. The accomplishment. of this object means that the detector units may be and congurations.

A` further object of the invention is the provision of a detector capable of accomplishing the above functions, yet of small. simple, light weight but rugged mechanical construction, requiring no electronic apparatus for its functioning, capable of use with any convenient potential orV frequency-of power supply, and designed to function without interfering ,with radio, radar or other electronic equipment carried by the aircraft.

which, l e tureg'rise indicator yset for a fixed temperature, contemplates makng lseparate temperature measurements in two the. inven-` or more zones within a given compartment and comparing the temperatures in each zone. Since any fire, at its outset, is localized and does not envelope the entire compartment, its presence will be indicated by a signiiicant differential existing between the temperatures noted in the different zones measured. ln the practical embodiment of the invention here disclosed, these measurements are automatically and continuously made and the comparison is continuously made by a balancing lever, so that the detector may be set to give an instant alarm whenever the difference in measured temperatures of the zones exceeds a selected value.

A fire detector comprising a preferred commercial embodiment of the present teachings is illustrated in the drawings of the specification, wherein:

Figure l is aplan view;

Figure 2 is an enlarged cross-sectional view taken substantially onithe plane of the line. 2-2 of Figure l;

Figure 3 is a plan sectional view taken substantially on the plane of the line 3-3 of Figure 2;

Figure 4 is adetail sectional view taken substantially on the plane of the line 4-4 of Figure 3;

Figure 5 is a sectional View on the line 5-5 of Figure 3',

Figure 6 is a sectional view similar to Figure 2, showing the movement of the parts in actuating a signal; and

Figures 7, 8 and 9 are diagrammatic illustrations of typical installations of the detector units.

As illustrated, the detector here shown consists of a housing or body portion 10 with a pair of slender temperature sensing arms 11 extending outwardly therefrom. It is contemplated that several of the units may be installed in the zone of possible fire, with the housings 10 mounted at any convenient spaced locations within the zone to be protected. -For example, in an aircraft nacelle, the sensing arms may be curved to surround or encircle the engine where they will be instantly exposed to any llame that might develop. The housings 10 are preferably of a corrosion resisting, high temperature metal such as stainless steel. As shown, they are of generally circular shape having a web portion with a center orifice 12, a pair of elongated slots 13 and recesses 14 between a switch chamber'15 on one side of the web and a differential chamber 16 on the opposite side.

The switch chamber is closed by a circular plate 17 seated against a shoulder 18 in the housing and held by a peripheral edge iiange 19 spun over the edge of the plate so as to provide a substantially air-tight switch compartment in which the electrical mechanisms of the unit are housed. The differential housing 16 is closed by a similar circular plate 21` seated on a shoulder 22 of the housing and held in place by a spun flange 23. As presently manufactured, the plates 17 and 21 are sealed with Glyptal applied to the shoulders and spun flanges, but it will 'oe apparent that, if desired, the unit may be hermetically sealed bypbrazing, soldering, or otherwise, and in this event it is contemplated that the apertures 14 may be utilized as chambers for silica gel to absorb any traces of moisture within the sealed housing. As shown, the plate 21 has a pair of outwardly extending bosses 24 on which mounting studs 25 are riveted. These may be threaded to facilitate mounting the unit.

The sensing arms 11 of the unit are of bimetallic construction, consisting of a slender exterior tube of metal such as stainless steel, for example, which may be secured within the bores 27 in the wall of the housing 1G by welding or otherwise, so that their inner ends are sealed. The metal of the tubes 26 has a relatively high degree of thermal expansion which greatly exceeds the coefiicient of expansion of the alloy wires 28 which extend through each tube. In the commercial embodiment of this invention the wire 28 comprises what is vknown in the trade as No. 42 Alloy, consisting of 42% nickel and the balance pure iron. The wires 28 are of a diameter a few thousandths of au inch less than the internal diameter of the tubes 26. These parts are lubricated for movement of the wires within the tubes by applying a graphite wipe to the wires prior to insertion. The outer extremities of the tubes 26 and the wires 28 are then welded together so that the differing rates of thermal expansion of the two metals will cause the inner ends of the wires to move inwardly or outwardly in response to changes in the temperature to which the sensing arms are subjected.

The inner ends of each of the wires 28 of the sensing arms 11 are secured within bores 29 in the head portions of a pair of operating pins 31 which have reduced end portions 32 tted into apertures in a iioating differential disc 33. The disc 33 is housed within the dilerential compartment 16 of the housing of the unit and has a center recess or orifice 34 which normally lies in coaxial relation with the orifice 12 of the housing. A stainless steel ball 35 is positioned in the opening 12 and extends into the orilice 34 of the disc 33, so that the ball tends to function as a center about which the diiferential disc 33 can pivot. the inside surface of the lower closure plate 21, and the disc is preferably provided` with an annular shoulder- 36 to reduce the area of contact and lessen friction in manner well understood in the art.

The switch housing 15 of the unit serves to house a snapacting switch consisting of a leaf spring flapper mounted on a screw threaded stud 3S and carrying a contact 39 at its free end. The switch apper is preferably of thin stainless steel and as shown includes a narrow center strip 37 with a pair of integral arms 41 on each side of the center strip and joined to it at the contact end. These arms are seated in V-notches 42 in a bifurcated yoke 43 carried by the stud 38. The notches 42 serve as pivot points for the ends of the spring arms 41, so that when the springs are exed to the position shown in Figure 2, the center portion 37 of the flapper is in tension and the side portions 41 act as compression elements to hold the contact 39 down, but whenever the center portion 37 ofthe switch ilapper is lifted across center these pivots cause the iiapper to snap upwardly.

The switch ilapper 37 is arranged to be actuated by the ball 35 which acts through an actuating ngerk44 mounted in the switch chamber 15 under the switch apper. The actuating linger includes a circular head portion 45 staked into a recess in the web of the housing 10, and a neck portion perforated at 46 to act as a pivot for the slender finger of the actuator. The iinger 44 of the actuator is provided with a longitudinal rib to give it considerable rigidity. The actuating finger 44 extends across the bore 12 in which the ball 35 rests, so that in the event the ball 35 is forced upwardly against the lower surface of the actuator strip, the strip will contact the center spring of the switch apper at the point 47 and lift the apper spring across the pivots 42. When this occurs, the flapper will snap upwardly to bring the contact 39 of the switch apper into engagement with its coacting contact 48. The contact 48 is carried by the upper plate 17 and is preferably provided with a mounting including a metal bushing 49 riveted into an aperture through the plate with a ceramic insulator 50 housed within the bushing so that a shank of the contact 48 may extend through the insulator and have a head portion 51 riveted over a ange of a terminal lug 52 from which electrical connections may be taken as desired.

In operation the device is not affected by changes of ambient temperature and responds only to a localized re affecting some point along the sensing arms. This is because the two opposite sensing arms are balanced against each other by a diierential mechanism. As shown, this comprises a simple balancing lever in the form of the disc 33 with a recess to receive the ball 35. Thus, as the arms 11 are exposed to changes in ambient temperature, the dilerent coefficients of expansion of the stainless steel vtubes 26 and alloy Wires 28 will cause the inner ends of the wires to move inwardly and outwardly, but the only result of this motion will be to rotate the disc 33 a few The lower surface of the disc 33 slides on degrees in one direction or the other about the ball 35, which then functions as a pivot for the disc; The sensing arms 1l are quite long, however, preferablyl each being almost a; yard in length so that when the detector is'installedinthe nacelle of an aircraft engine, by way of eX- ample, any fire breaking out in the engine will not aifect the entire unit equally but will only aect a portion of one of theV arms lying in the fire zone. Should this occur, the increased expansion of the stainless steel tube 26 on the arm extending into the tire will draw the wire 23 outwardly and exert a force on one of the pins 3l which is not balanced by a corresponding movement of the other pin. When this occurs, the upper edges of the recess 34 in the differential disc 33 will exert a camming action on the spherical surface of the ball 35 to move it upwardly against the actuating linger 44. This nger will bear against the spring dapper of the switchY to push it over center. The snringflapper will then snapuupwardly to close the contacts'39'/;-S and give the alarm signal.

With this type of construction the sensing arms may be very slender and quiteV flexible so that the expansion occurs almost instantaneously uponv exposure to the llame. This results in an extremely quick response, tests having shown that the unit often gives a response in less than two seconds and never fails'to respond in less than an interval of five seconds, even though only a relatively small fraction of the length of one or" the arms is exposed to the heat of the flame.

it is'also to be noted that since the differential coupling of the opposite sensing arms balance out any variations in ambient temperature, the unit acts in response to a given deviation from ambient temperature rather than at a xed temperature setting. The differential at which the switch closes may be selected as desired, but should be greater than slight temperature variations that might arise from causes other than lire. Thus, the mechanism is not subject to false signals even under abnormal operating conditions. This is true even though the temperature throughout the entire engine compartment may reach extremely high levels, but the unit is nevertheless capable of instant response if anV actual fire breaks out. Similarly, the unit is equally well suited to sounding an alarm in the event that a re breaks out in the initial starting or" an engine even though all of the parts within the nacelle may be at a sub-zero temperature;

The form of a detector here shown is not only capable of uniform operation within extremely wide limits of temperature, altitude, and humidity but is also unaffected by changes in atmospheric pressure. lt cannot be harmed by corrosion, nor by exposure to rain, salt spray, or'immersion in fuel or oil. it is impervious to exposure to dust, wind, and driven sand. it is not harmed by long continued vibration, nor by forces of violent acceleration or deceleration.

The detector here shown is able to give an almost instant signal in the event of a llame in any portion or the engine fire is extinguished. All parts of the unit are capable of withstanding severe extremes in both heat and cold, and as a matter of fact, have by actual test shown themselves capable of withstanding sustained temperatures of 2,000" F yet retaining their functional ability.

When only a short length of one of the sensing arms is exposed to llame, the movement of the parts is comparatively small, as shown in Figure 6. if the entire length of the arm is exposed, the movement will be correspondingly greater, and may cause the disc 33 to ride under the ball 35 so that the ball rests on the fiat surface of the disc. As the sensing arms cool, however, the disc is returned to centered relationship. Thus even extreme movements do not damage the switching mechanism.

The detectors may be mounted in any convenient location and may be used singly or in various arrays to adequately cover a zone to be protected. Normally, the

sensing arms will be balanced so that an alarm is sounded if the temperature of one exceeds the otherby a selected The installation may be reversed, however, to,

amount. give an alarm when the temperatures of the two arms ap- Sia and the rear sensing unit Sib are isolated from each other. When so isolated, a flame cannot aiect the two arms equally, ,no matter what the location of the llame. in an installation of this character it will be noted that the` sensing unit Sla, and if it breaks out in the aft compartment it will` affect onlythe. arm 81h. It follows that in either case the baffle 82 prevents the possibility of a llame raising the temperatures of the two differential arms equally and thus makes for the dependable functioning of the` system.

lf desired,l the units may have the temperature sensing arms curved as shown in Figure 7 so that. the four detecting; units 62, 63, 61s and 65 completely encircle the compartment in which a radial engine isrnounted, or they may beV arranged in a continuous straight line as exempliiied by the detectors 7l to 75 in Figure 8. The advantages following employing systems of these types are more fully pointed out in our copending disclosure Serial No. 94,221, filed on even date herewith, now FatentNo., 2,563,904.

While we have disclosed what we believe to be a new. methodv of detecting res and have described a Vpresent preferredv embodiment of a device for practicing our teachings in this respect, we are aware that numerous variaparting from the inventive concept nor sacrificing all of the advantages thereof, and we therefore point out that the scope of the present invention is not limited to the precise'form of device here illustrated, but extends equally to anyvaration or modication thereof coming within the terms of the appended claims.

Having thus described the invention, what we claim as new and desire to protect by United States Letters Patent is: y

l. A re detector comprising a sealed housing having an insulated electrical connection extending into the housing and an electric switch within the housing; a pair of sensing arms consisting of a continuous, long, slender tube of metal having a high coelicient of expansion, with aV wire of alloy having a low coeiicient of expansion exten-ding through the tube and extending into the housingthe tubes of saidsensing elements being sealed to the housing and the outer extermitzes of the tubes and efficient of expansion, with a wire of alloy having a low coelcient of expansion extending through the tube, the outer extremities of the tubes and alloy wires being joined to each other, with the alloy wires extending into the housing and operatively connected to a diierential mechanism comprising a lever, a pivot recess in said differential mechanism, and a ball seated in the recess and mechanically interconnected with the electric switch whereby differential expansion of the temperature sensing elements will shift the dierential mechanism and ball to actuate the switch.

3. A re detector comprising a housing with an electric switch; a pair of bimetallic temperature sensing arms extending in dierent and Opposite ldirections from the housing, each of said temperature sensing arms consisting of a long, slender metal tube with a wire extending through the metal having a diiierent coefficient of expansion joined to the tube at the outer end, and extending into the housing; said Wires being attached to shiftable pins pivoted to a diierential lever; a pivot recess in said diierential lever and a pivot comprising a ball shiftably mounted in a bore of the housing with a portion of the ball extending into the pivot recess of the differential lever, with the ball mechanically interconnected with the electric switch whereby dierential expansion of the temperature sensing elements will shift the diierential lever and ball to actuate the switch.

4. A re detector comprising a sealed housing having an insulated electrical connection extending through into the housing wall with an electric switch within the housing; a pair of temperature sensing devices extending in dierent directions from the housing, each of said temperature sensing devices having a shiftable temperature responsive element extending into the housing and operatively connected to a shiftable differential mechanism comprising a lever; a pivot recess in said -diierential lever and a pivot comprising a ball shiftably mounted in a bore of the housing with a portion of the ball extending into the pivot recess of the differential lever and the opposite side of the ball mechanically interconnected with the electric switch whereby differential movement of the temperature responsive elements of the sensing devices will shift the dierential lever and bail to actuate the switch.

5. A iire detector comprising a sealed housing having a switch compartment, a differential compartment, and a central bore extending between said compartments; an insulated electrical connection extending into the switch compartment of the housing wall and an electric switch within the housing; a pair of temperature sensing devices extending to points remote from the housing and spaced apart from each other; each of said sensing devices having a shiftable temperature responsive element extending into the differential chamber of the housing and operatively connected to a shiftable differential lever having a pivot recess carried on a pivot comprising a ball shiitably mounted in the bore extending between the differential compartment and switch compartment of the housing; with a portion of the ball extending into the pivot recess of the diiierential lever and the opposite side of the ball mechanically interconnected with the electric switch whereby differential movement of the temperature responsive lelements of the sensing devices will shift the diiferential lever and ball to actuate the switch.

6. A iire detector comprising a plurality of continuous birnetallic temperature sensing devices oppositely disposed in end to end relationship extending into zones spaced apart from each other, each of said devices including a shiftable element responsive to variations in temperature, a differential mechanism mechanically interconnecting said shiftable elements whereby movements of said elements are balanced at equal temperatures, cam means responsive to diiierential movement of said elements, and an electrical switch operated by said cam means to actuate a signal.

7. A tire detector comprising a plurality of temperature sensing devices spaced apart from each other, each of said devices includinga shiftable element responsive to variations in temperature, a diierential mechanism mechanically interconnecting said shiftable elements `whereby movements of said elements are balanced at equal temperatures, cam means responsive to diierential movement of said elements, and an electrical switch operated by said cam means to actuate a signal.

8. A tire detector comprising a plurality of temperature sensing devices, each having a shiftable temperatureresponsive element; together with a mechanical diierential mechanism consisting of a oating lever interconnecting said shiftable temperature responsive elements and balancing the movements thereof at equal temperatures of the sensing devices, and means responsive to an increase in the temperature of one of said sensing devices over another to actuate said mechanical differential mechanism to actuate a signal.

9. A tire detector comprising a housing with a plurality of temperature sensing devices, each consisting of a long slender flexible metal tube with one end of the tube secured to said housing, the tube having a shiftable temperature responsive element consisting of a ilexible wire extending through the tube, said wire being of metal having a dierent coeicient of expansion than the tube and joined to the tube at its outer end with the inner end of said wire extending into the housing; together with differential means interconnecting said wires, and responsive to an increase in the temperature of one of said temperature sensing devices over another to actuate a signal.

l0. A fire detector comprising a housing with a plurality of elongated continuous temperature sensing devices oppositely disposed in end to end relationship extending into zones spaced apart from each other, together with diierential means to compare the temperatures to which said sensing devices are subjected, and means responsive to an increase in the temperature of either one of said sensing devices over the other to actuate a signal.

ll. A fire detector comprising a plurality of temperature sensing devices, each of said sensing devices consisting of a relatively long slender flexible metallic tube, the said tubes each having one end thereof secured to the housing and dii/erging therefrom in different directions together with diierential means to compare the temperatures to which said sensing devices are subjected, and means responsive to an increase in the temperature of Y either one of said sensing devices over the other to actuate a signal.

12. A iire detector comprising a plurality of temperature sensing devices spaced apart from each other, together withV a mechanical diiierential mechanism interconnecting said sensing devices to continuously compare the temperatures to which said devices are subjected, an

electrical switch and means responsive to an increase in the temperature of either one of said sensing devices overthe other to operate said switch and actuate a signal.

13. A iire detector comprising a plurality of temperature sensing devices oppositely disposed in end to end relationship; each of said sensing devices consisting of a relatively long slender iiexible metallic tube, the said tubes each having one end thereof secured to the housing and diverging therefrom in different directions whereby the ends of said tubes are widely spaced apait from each other, together with differential means interconnecting said sensing devices to continuously compare the temperatures to which said sensing devices are subjected, and means responsive to an increase in the temperature of either o-ne of said sensing devices over the other to actuate a signal.

i4. The method of detecting fires consisting of mechanically measuring the temperature at two zones spaced apart from each other; mechanically comparing the temperature measurements of said zones, and automatically actuating a signal when the temperature measured in either one of said zones exceeds the temperature measure in the other by a selected amount.

l5. A iire detecting device comprising, in combination, a plurality of continuous bimetallic temperature sensing devices extending into different zones having substantially the same temperature under normal conditions but spaced apart from each other, each of said devices including a shiftable element responsive to variations in temperature; a diierential mechanism mechanically interconnecting said shiftable elements whereby movements of said elements are balanced at equal temperatures, means responsive to differential movement of said elements to actuate a signal, and means to isolate the said bimetallic temperature sensing devices from each other, said last named means compn'sing a re wall intermediate the ends of said ternperature sensing devices.

16. A fire detecting device comprising, in combination, a plurality of continuous bimetallic temperature sensing devices extending into different zones ha 'ng substantially the same temperature under normal conditions but spaced apart from each other, each of said devices including a shiftable element responsive to variations in temperature; a dierential mechanism mechanically interconnecting said shiftable elements whereby movements of said elements are balanced at equal temperatures, means responsive to differential movement of said elements to actuate a signal, and means to isolate the said bimetallic temperature sensing devices from each other.

17. A fire detecting device comprising, in combination, a plurality of temperature sensing devices extending into diierent zones having substantially the same temperature under normal conditions but spaced apart from each other, differential means to compare the temperatures to which said sensing devices are subjected, means responsive to an increase in the temperature of one of said temperature sensing devices over another to actuate a signal, and means to isolate the said sensing devices from each other; said last named means comprising a re wall intermediate the ends of said temperature sensing devices.

18. A tire detecting device comprising, in combination, a plurality of temperature sensing devices extending into dierent zones having substantially the same temperature under normal conditions but spaced apart from each other, differential means to compare the temperatures to which said sensing devices are subjected, means responsive to an increase in the temperature of one of said temperature sensing devices over another to actuate a signal, and means to isolate the said sensing devices from each other.

19. A re detecting device comprising a re Wall and a plurality `of temperature sensing devices, said sensing devices being positioned on opposite sides of the re Wall whereby they are subject to temperatures in different zones having substantially the same temperature under normal conditions; together with differential means to compare the temperatures to which said sensing devices are subjected, and means responsive to an increase in the temperature of one of said sensing devices over another to actuate a Signal.

References Cited in the le of this patent UNITED STATES PATENTS 1,205,434 Connell Nov. 21, 1916 1,450,125 Webb Mar. 27, 1923 1,573,033 Bishop Feb. 16, 1926 1,780,302 Koch et al. Nov. 4, 193,0 2,037,155 Stuart Apr. 14, 1936 2,067,959 Wasson Ian. 19, 1937 2,088,485 Schoepr" uly 27, 1937 2,299,533 Cyr Oct. 20, 1942 2,385,487 Baughman Sept. 25, 1945 FOREIGN PATENTS 401,667 Germany Sept. 8, 1924 

